Mountain crash claims three

The commercial pilot and two passengers were on a cross-country flight in a Cessna 182. The trip included flying through a narrow mountain pass near Nikolai, Alaska.

The typical route through the pass required making multiple turns, and the pass intersected with a box canyon.

A family member reported the airplane overdue for arrival, and an alert notice was issued. The airplane’s wreckage was located the following day at the bottom of the box canyon.

A pilot who flew through the mountain pass on the morning of the accident reported 4,400-foot ceilings, severe turbulence, and flat light conditions.

A friend of the pilot who attempted to cross the mountain pass the day of the accident reported flat light conditions and having difficulty discerning terrain features. He turned the airplane around due to the weather conditions and returned to the airport. He also stated that the accident pilot had become disorientated the previous year while flying a helicopter through the same mountain pass and had taken the wrong route.

Investigators determined that given the lack of mechanical anomalies, the reported weather conditions, and the pilot statements, it is likely that the pilot mistakenly entered the box canyon thinking it was his route.

Additionally, wreckage impact signatures and GPS data indicated that it is likely that the pilot was attempting to avoid rising terrain by entering a steep bank turn, which resulted in an aerodynamic stall.

The NTSB determined the probable cause of the accident as the pilot’s failure to maintain adequate airspeed while maneuvering inside a box canyon and the airplane’s subsequent aerodynamic stall, which resulted in an in-flight collision with mountainous terrain. Contributing to the accident was the pilot’s visual disorientation in flat light conditions.

Comments

Flat light is an optical illusion, also known as “sector or partial white out.” It is not as severe as “white out” but the condition causes pilots to lose their depth-of-field and contrast in vision. Flat light conditions are usually accompanied by overcast skies inhibiting any good visual clues. Such conditions can occur anywhere in the world, primarily in snow covered areas but can occur in dust, sand, mud flats, or on glassy water. Flat light can completely obscure features of the terrain, creating an inability to distinguish distances and closure rates. As a result of this reflected light, it can give pilots the illusion of ascending or descending when actually flying level. However, with good judgment and proper training and planning, it is possible to safely operate an aircraft in flat light conditions.

In all my years of aviation, now almost 50 years, this is the first time I can recall coming across this terminology “flat light conditions.” Such words are meaningless buzz words to me into which I suspect one can pour whatever meaning one chooses. I understand restrictions to visibility or inadequate lighting but not “flat light conditions.”